What is a 'donut' used for in lighting equipment?

In the context of lighting equipment, a 'donut' is used primarily to sharpen the focus of a light. This accessory is typically composed of a ring of material that can be placed around a lighting fixture to prevent light spill and control the beam spread. By doing this, the donut enhances the precision of the light beam, focusing it onto a specific area or subject, which is essential in theatrical performances where specific lighting is required to highlight actors or particular scenes.

Items such as softboxes and diffusion filters serve different purposes, such as softening or diffusing light, but a donut's main role aligns with concentrating and defining light for greater control in stage settings.